So by default, the default servlet is loaded at webapp startup and
directory listings are disabled and debugging is turned off.

What can I change?

The DefaultServlet allows the following initParamters:

Property

Description

debug

Debugging level. It is not very useful unless you are a tomcat
developer. As
of this writing, useful values are 0, 1, 11, 1000. [0]

listings

If no welcome file is present, can a directory listing be
shown?
value may be true or false [false]
Welcome files are part of the servlet api.
WARNING: Listings of directories containing many entries are
expensive. Multiple requests for large directory listings can consume
significant proportions of server resources.

precompressed

If a precompressed version of a file exists (a file with .br
or .gz appended to the file name located alongside the
original file), Tomcat will serve the precompressed file if the user
agent supports the matching content encoding (br or gzip) and this
option is enabled. [false]
The precompressed file with the with .br or .gz
extension will be accessible if requested directly so if the original
resource is protected with a security constraint, the precompressed
versions must be similarly protected.
It is also possible to configure the list of precompressed formats.
The syntax is comma separated list of
[content-encoding]=[file-extension] pairs. For example:
br=.br,gzip=.gz,bzip2=.bz2. If multiple formats are
specified, the client supports more than one and the client does not
express a preference, the order of the list of formats will be treated
as the server preference order and used to select the format returned.

readmeFile

If a directory listing is presented, a readme file may also
be presented with the listing. This file is inserted as is
so it may contain HTML.

globalXsltFile

If you wish to customize your directory listing, you
can use an XSL transformation. This value is a relative file name (to
either $CATALINA_BASE/conf/ or $CATALINA_HOME/conf/) which will be used
for all directory listings. This can be overridden per context and/or
per directory. See contextXsltFile and
localXsltFile below. The format of the xml is shown
below.

contextXsltFile

You may also customize your directory listing by context by
configuring contextXsltFile. This must be a context
relative path (e.g.: /path/to/context.xslt) to a file with
a .xsl or .xslt extension. This overrides
globalXsltFile. If this value is present but a file does
not exist, then globalXsltFile will be used. If
globalXsltFile does not exist, then the default
directory listing will be shown.

localXsltFile

You may also customize your directory listing by directory by
configuring localXsltFile. This must be a file in the
directory where the listing will take place to with a
.xsl or .xslt extension. This overrides
globalXsltFile and contextXsltFile. If this
value is present but a file does not exist, then
contextXsltFile will be used. If
contextXsltFile does not exist, then
globalXsltFile will be used. If
globalXsltFile does not exist, then the default
directory listing will be shown.

Is this context "read only", so HTTP commands like PUT and
DELETE are rejected? [true]

fileEncoding

File encoding to be used when reading static resources.
[platform default]

sendfileSize

If the connector used supports sendfile, this represents the minimal
file size in KB for which sendfile will be used. Use a negative value
to always disable sendfile. [48]

useAcceptRanges

If true, the Accept-Ranges header will be set when appropriate for the
response. [true]

showServerInfo

Should server information be presented in the response sent to clients
when directory listing is enabled. [true]

How do I customize directory listings?

You can override DefaultServlet with you own implementation and use that
in your web.xml declaration. If you
can understand what was just said, we will assume you can read the code
to DefaultServlet servlet and make the appropriate adjustments. (If not,
then that method isn't for you)

You can use either localXsltFile or
globalXsltFile and DefaultServlet will create
an xml document and run it through an xsl transformation based
on the values provided in localXsltFile and
globalXsltFile. localXsltFile is first
checked, followed by globalXsltFile, then default
behaviors takes place.